Ink jet printing system using ion charging of droplets

ABSTRACT

There is described an arrangement for charging with ions the drops in an ink drop printing apparatus, in place of the present induction charging techniques which are employed.

D United States Patent 1 [111 3,769,627 Stone 5] Oct. 30, 1973 INK JET PRINTING SYSTEM USING ION [56] References Cited CHARGING OF DROPLETS UNITED STATES PATENTS [75] Inventor: Joseph J. Stone, Northbrook, Ill. 3,596,275 7/1971 Sweet 346/75 X z A. [73] Asslgnee B Dlck GNP-pally Chicago Primary Examiner-Joseph W. Hartary [22] Filed: Dec. 13, I972 Attorney-Samuel Lindenberg et al.

21 A 1. No.2 314 512 1 pp 57 ABSTRACT There is described an arrangement for charging with if i 346/75 bifig l ig ions the drops in an ink drop printing apparatus, in 51 74 Es. place of the present induction charging techniques e o earc 317/3, which are employed 13 Claims, 3 Drawing Figures PHOTO POSlTH/E CELL CORONA EaOURCF. T

T i 48 H\/ PuLsE 2 GEN i {82 7 ADJU5TABLE P05 2 P05 3x 05 4P0s 5 P05 TIME 'SHlFT Sl-HFT SHlFT SHlFT SHWT DELAY REG REG RE6 REG: REG

1 l l T Sl-H FT PULSEE Tl NHNG PULEzE A/D CONVERTER DROP CHARGE CONTROL SOURCE +OFF 60 N POSlTlVE v CORONA AMP S URCE- I l-9 2 HV 92 I w 1L \1 2 Posmvg 6Q L CORONA ADJUFJT'ABLE 62- SOURCE TIME I DELAY +7 Hv r DROP CHARGE j CONTROL SOURCE VlDEO COUNTER DATA souma INK JET PRINTING SYSTEM USING ION CHARGING OF DROPLETS BACKGROUND OF THE INVENTION This invention relates to ink drop printing apparatus, and more particularly, to an improved arrangement for charging ink drops.

Present ink drop printing systems, such as described by Sweet in his US Pat. No. 3,596,275, use selectively charged droplets, which are deflected by a'high voltage deflection field to form images on a recording medium. These droplets form at a very regular rate by squirting pressurized ink through a small orifice. Ultrasonic energy, superimposed on the supply pressure for the ink, velocity modulates the emitter stream. As a result of this modulation, the stream forms into droplets at the frequency of the ultrasonic source.

Selective drop charging involves the induction of charges in the drop being formed by a surrounding charged electrode. The induced charge varies in accordance with the inducing voltage until the instant in time at which the droplet physically separates from the stream. From that time on, the induced charge is trapped and remains with the drop. It is obvious, therefore, that the charging process must be carefully synchronized with the timing of the drop break off. This involves the use of complex phasing control sensors and loops. This in turn, increases the cost of the equipment.

OBJECTS AND SUMMARY OF THE INVENTION It is an object of this invention to provide an ink drop charging system which does not depend upon a synchronization of the carging charging with the break off time.

It is another object of this invention to produce an ink drop charging system, which charges drops after they break off from the ink jet stream.

Another object of the present invention is the provision of'a simpler and less complex ink drop charging system than has been used heretofore.

These and other objects of the invention may be achieved by an arrangement wherein drops, after they separate fron the ink jet stream, are detected and charged by ions to a level indicated by the video signals, which is determined by the location on the paper on which it is desired to deposit the drop. The drops, after charging, pass through an electric field which deflects each drop by an amount determined by the amplitude of the charge thereon.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is aschematic diagram of a portion of an ink jet printer. The portion shown in the ink drop charging and deflecting arrangement, which is in accordance with this invention. The reason why an entire ink drop printing system is not shown is because, aside from the of a control apcharging portion which is in accordance with this invention, these printing systems are well known, are commercially available, and are described in a number of patents, besides the Sweet patent referred to previously herein.

A pressurized ink supply, not shown, causes ink to flow through a nozzle 10. The nozzle has a small opening 12 through which an ink jet is emitted. An oscillator 14 applies electrical energy at a suitable ultrasonic frequency to a transducer 16. The transducer converts this electrical energy to mechanical energy and usually squeezes the nozzle at a rate determined by the oscillator frequency. As a result, the stream 18 of ink, which is emitted, forms into drops such as 29 through 34. Light from a source 40 is focused by a lens 42 at the region through which the drops pass. The drop 22 is in position to intercept or block the light. Another lens 44 focuses light from the region through which the drops pass onto a photocell 46. The photocell output is applied to a pulse generator 48, which generates a pulse each time the light is blocked by a drop. The output of the pulse generator 48 is used for timing and control purposes in such a manner that one pulse occurs for each drop passing the detection zone, or the region at which light is focused by the line 42.

It should be noted that the ink jet stream breaks up into a series of uniformly spaced, equally sized drops, moving at a constant velocity toward the recording medium. The initial ink stream pressure directly determines the drop velocity and this can be regulated within close limits. 1

Immediately following the photocell detector, each drop passes over a series of charging apertures 50, 52, 54, 56 and 58. Each of these apertures permits charges to be placed on a drop by means of gaseous ions emitted from a positive corona source 60. Control voltages which determine whether or not ions can pass through one of the apertures 50 through 58, are received from amplifiers, respectively 62 through 70,.which are applied to conductive layers adjacent each aperture. Details of the control of each aperture will be described in connection with FIG. 2, subsequently herein.

Each of the amplifiers 62 through is driven by the output stage-of the respective shift registers 72 through 80. Each one of the'shift registers is one or more bits in length and shifts, in response to shift pulses received from an adjustable time delay circuit 82. The adjustable time delay circuit is driven by the output of the pulse generator 48 and not only provides shift pulses, but provides timing pulses to the remainder of the system. The adjustable time delay is used to delay the output of the pulse generator 48, which is applied thereto for whatever interval is required to insure that a drop is positioned over each one of the respective apertures 50 through 58. Once this interval is set,'since the drops occur at regular intervals and are regularly spaced, it need not be adjusted again, unless either the ink jet pressure or the oscillator frequency is altered.

In order to block the flow of gaseous ions through an aperture, a negative voltage is applied to the conductive layer 82, which surrounds an aperture. Otherwise, a positive voltage is applied to this conductive layer.

Let it be assumed that it is desired to charge a drop with three increments of charge as it passes over the five holes. This will require that, for example, when drop 26 is over aperture 50, a one representative control voltage is applied to the conductive layer around the hole 50. Similarly, when drop 26 is over the holes 52 and 54, one representative voltage should be applied to the conductive layer surrounding each of these holes. When drop 26 then successively passes over the holes 56 and 58, zero representative voltages should be applied to the conductive layers surrounding openings 56 and 58. The zero representative layers will be negative signals and the one representative layers will be positive signals. This will require that one representative signals be at theoutput stages of shift registers 72,

74 and 76, when ink drop 26 successively passes over,

openings 50, 52 and 54. This further requires that zero representative signals be at the output stages of shift registers 78 and 80, when ink drop 26 is opposite the respective openings 56 and 58.

Since the shift pulses are applied to cause the shift registers to shift as each drop passes between the lenses 42 and 44, the loading of the shift registers with the signals which are to control the charging of drop 26, (and other drops also), must be as follows. Assuming that the shift registers are five stage registers, and the respective stages from output to input are numbered from zero through four, a one representative signal is in stage zero of shift register 72, a one representative signal is in stage one of shift register 74, a one representative signal is in stage two of shift register 76, a zero representative signal is in stage three of shift register 78, and a zero representative signal is in stage four of shift register 80. e

The loading of signals into the shift registers for controlling the charging of drops must be done in the staggered manner described, so that a'drop is properly charged as it passes by each one of the five openings. One way of achieving this type of loading is by having suitable different delay lines in front of the shift registers. Another preferred way is to make the shift registers have different lengths so that although they are loaded in'parallel, the control voltage forcharging a drop will arrive at the shift register output stages properly timed as the drop successively passes each charging aperture. A third wayisto-have the shift registers the same length, say one stage, but to have a counter count the output of the adjustable time delay and apply the first count output toshift register 72; the second countoutput is applied to shift register 74; the third count output "is applied to shiftregister 76; the fourth count output is applied to shift register 78 and the fifth count output is applied to shiftregister 80.

Thus, for-each droplet, a number of shift pulses must be provided equal to'the number of apertures to be controlled. The time between pulses should equal the flight time of the individual droplets between apertures,

, and the start of the pulse train should occur at the time the detected drop reachesthefirst aperture.

The output of the adjustable time delay circuit 82 is not only applied to the shift registers to provide shift pulses, but is also applied to a drop charge control source 84, which is drivenby signals from a data source 86. The data source and the drop charge control source function in the manner of the circuit used in presently manufactured drop charging systems in that they function to producea sequence of charging voltages for each character to be printed having amplitudes which, when applied to the drops will cause the drops to be deposited in a pattern representative of a character. All that is needed to produce a pattern of controlvoltages for controlling the apertures 50 through 58 for ion charging is an analog-to-digital converter 85, which converts the analog charging voltages into five digital control voltages. These are applied to the five shift registers 72 through 80.

The system shown may also be .used for printing curves or lines, since in that case, the data source will provide succession of signals which the drop charge control source will convert into voltages that are then converted into digital aperture control signals by the analog-to-digital converter, whereby a drop will be charged and thereafter deflected by a distance representative of that voltage.

In the event that the system is used for printing characters, then the output of the adjustable time delay circuit is applied to a counter 88. Since a character in order to be printed requires a number of drops, the counter counts the number of drops passing between the lenses 42 and 44, representative of the maximum number of drops for printing a character, and then applies an output to the data source 86 to apply the next set of signals representing a character to be printed to the drop charge control source. The drop charge control source in response to the timing pulses generates a sequence of voltages required to charge drops in the induction type of charging for depositing the drops in the form of a character. in the present invention, this voltage sequence is applied to the analog-to-digital converter as described above.

It will be appreciated that where purely a curve or line printing system is desired, that is where a single ink drop is to represent each data signal, as opposed to where a plurality of drops are required, then, the counter 88 is omitted.

After the drops have receivedcharges in passing over the apertures 50 through 58, they pass between two spaced parallel electrodes respectively 90, 92. These two electrodes are connected to a source of potential, with the lower electrode 92 being connected to ground andthe-upper electrode 90, being connected to a negative high voltage source to establish an electric field between the electrodes. Drops which are not charged are vnot deflected and move along in the path into which they were initially-projected. These drops are finally deflected -.by a catcher 94, into areservoir 96, from which theymay be pumped back tothe initial reservoir used for this system. The other drops, which bear charges, are deflected by the field by an amount determined by the amplitude of the charge. The drops finally fall on the recording medium 98. Suitable mechanisms are provided for moving the recording medium, in a well known manner, to insure that the pattern in which the drops fall thereon forms either characters or curves, as desired.

FIG. 2 is an enlarged cross sectional view of the region around one of the apertures, such as the aperture 50. The lower conductor 82, which serves as a control electrode, surrounds the aperture and a control voltage is applied thereto from an amplifier 62. The lower con ductor 82 is separated from the deflection plate 92, by a suitable insulator 100. The deflecting electrode 92 is connected to ground. The amplifier'62 applies a negative voltage relative thereto when it is desired to block the passage of ions through the opening, and a positive voltage relativetherethrough, when it is desired to permit the passage of ions'through the opening.

The positive coronasource '60 generates positive ions. A field B, may be established between the positive corona source and the control electrode 82 such that these ions are accelerated towardcontrol electrode 82. When the control electrode is positive, ions are urged through the opening and when the control electrode is negative, ions are not urged through the opening. A field E is established by the relative potentials between the electrode 92 and the conductor 82. When the con-.

ductor 82 is negative with respect to the conductor 92, this field blocks the ions through the opening. A third field E is established between the electrode 92 and the electrode 90 which projects ions out of the opening and toward the electrode 90. Any ink drops that is in the space between electrodes 90 and 92, and that is over an opening through which the ions pass, will be bornbarded with ions and thus, will assume a positive charge.

show an arrangement for charging drops with different amplitude, using a single hole. The structures in FIG. 3, which perform the same function as the structures in FIG. I, bear the same reference numerals. The change between the drawing of FIG. 1 andthat of FIG. 3 is in the omission of the analog-to-digital converter 85 and the five registers 72 through 80. The output of the Drop Charge Control Source is a signal whose amplitude is determined by a signal from the video data source. This apparatus is the same as is used presently for the inductor charging of drops. The output of the drop charge control apparatus is applied to the amplifier 62, which after amplification, appliesit to the control electrode 82 .'Only a single opening 50 is used. The amount of ion charge on a drop passing adjacent opening 50 is determined by the'amplitude of the voltage applied to the control electrode 82. As was previously the case, the distance of the deflection of the 'drop from the trajectory of an uncharged drop.

It should be appreciated that in FIG. 1, the five charging holes which are shown are by way of example. More or less may be used as desired. Also, the system illustrated herein uses a positive corona source. Those skilled in the art will appreciate that a negative corona source may also be used, by reversing all the voltage polarities shown in FIG. I.

There has accordingly been described and shown herein a novel and useful arrangement for charging drops with ions.

What is claimed is:

1. In an ink drop printing system of the type wherein drops of ink are formed in a serial stream, and are emitted along a path toward a recording medium, said drops have charges applied to them in accordance with signals from a video source at a charging position along said path, said drops thereafter passing between two deflection electrodes which deflect the drops a distance determined by the amplitude-of the charges thereon, and said drops finally coming to rest upon said recording medium, the improvement in charging said drops comprising:

a source of ions,

means for establishing a field for bombarding each drop with ions as it passes through said charging position, and means for applying signals from said video source to 5 said means for establishing a field for controlling said field for determining the amount of charge on each drop.

2. In an ink drop printing system as recited in claim 1 wherein there is included:

means responsive to the presence of ink drops at a location prior to said charging position for generating timing signals responsive thereto, and

means for timing the application of signals for controlling said field responsive to said timing signals.

3. In an ink drop printing system as recited in claim 1 wherein said means for establishing a field comprises: blocking means interposed between said source of ions and the path of said drops at said charging position to block the access of ions from said source from said path of said drops,

said blocking means having an aperture therethrough sized to afford ions access to a drop at a time, and

a first conductive means surrounding said aperture on the side of said blocking means adjacent said source of ions,

said means for applying signals from said video source to said means for establishing a field includes: v 1

means for applying said signals between said source ofions and said first conductive means surrounding said aperture.

4. In an ink drop system as recited in claim 3 wherein said means for establishing a field for bombarding each drop with ions further includes:

a second conductive means surrounding said aperture on the side of said blocking means, adjacent the path of said drops,

a third conductive means positioned opposite said second conductive means and spaced therefrom to permit said stream of drops to pass therebetween, and i f means for biasing said second and third conductive means relative to said first conductive means to establish fields which direct ions entering said aperture at the path of said drops.

5. In an "ink drop system as recited in claim 1 wherein said means for bombarding each drop with ions as it passes through said charging position includes:

a blocking means interposed between said source of sition to block the access from said source from said path of said drops,

said blocking means having a plurality of apertures therethrough'and spaced along the path of said drops and sized to afford ions access successively to a drop as it moves along said path through said charging position, and

a separate first conductive means surrounding each of said plurality of apertures on the side of said blocking means adjacent said source of ions,

said means-forapplying said signals from said video source to said means-for establishing a field includes,

analog-to-digital means for converting each of said signals from said video source into a binary code having as many bit signals as there are apertures in said blocking means, and

ions and the path of said drops at said charging pomeans for applying the bit signals representative of a video signal between said source of ions and each of said separate first conductive means successively to charge a drop passing through said charging position.

6. In an ink drop system as recited in claim wherein said means for applying the bit signal representative of a video signal between said source of ions and each of said separate first conductive means successively includes:

a shift register for each of said plurality of apertures,

means for applying the output of each shift register to a separate one of said first conductive means,

means for applying each bit signal to the input of a different one of said shift registers,

means for detecting the presence of a drop prior to its entrance into said charging position, and producing a timing signal representative thereof, and

means for applying said timing signal to each of said shift registers to cause them to advance responsive thereto. I

7. In an ink drop printing system of the type wherein drops of ink are formed in a serial stream, and are emitted along a path toward a recording medium, said drops have charges applied to them in accordance with signals from a video source at a charging position along said path, said drops thereafter passing between two deflection electrodes which deflect the drops a distance determined by the amplitude of the charges thereon,

and said drops finally coming torest upon said recording medium, the improvement in charging said drops comprising:

a source of ions, conductive grid means interposed between the source of ions and said charging position, and means for applying signals from said video source to said conductive grid means for controlling responsive thereto the amount of ions which can pass through said conductive grid means to charge a drop passing through said charging position. 8. ln an ink drop system as recited in claim 7 wherein said conductive grid means comprises:

an insulating blocking means having an aperture therethrough, and conductive means surrounding said aperture on each surface of said insulating blocking means. 9. In an ink drop system as recitedin claim 7 wherein said conductive grid means comprises:

an insulating blocking means having an aperture therethrough, v a separate conductive'means surrounding each aperture on the surface of said insulating blocking means adjacent said ion source, and a conductieve means surrounding each aperture on the other side.

10. In an ink drop system as recited in claim 9 wherein said means for applying signals from said video source to said conductive grid means comprises:

means for converting each of said signals from said video source into a binary code having as many bit signals as there are apertures in said insulating blocking means,

means for applying the bit signals representative of a video signal between said source of ions and each of said separate conductive means successively to charge a drop passing through said charging position.

11. In an ink drop system as recited in claim 10 wherein said means for applying the bit signals representative of a video signal between said source of ions and each of said separate conductive means successively includes:

means responsive to the presence of drops prior to entering said charging position for generating timing signals, a separate delay means for each aperture, each delay means having its input connected to receive one of the bit signals in a binary code representative of a video signal and its output connected to apply a bit signal to a separate one of said separate conductive means, and

means for applying said timing signals to each of said separate delay means to enable said separate delay means to successively apply a bit signal to a conductive means as a drop passes the aperture surrounded by said conductive means.

12. ln an ink drop system as recited in claim 8 wherein there is included a further conductive means positioned opposite said insulating blocking means at said charging position to permit drops to pass therebetween, and

means for applying a potential between said further conductive means and said conductive means surrounding the apertures of said insulating means to establish an electric field therebetween for enabling ions passing through said aperture to bombard a drop opposite said aperture.

13. In an ink drop system as recited in claim 9 wherein there is included a further conductive means positioned opposite said insulating blocking means at said charging position to permit drops to pass therebetween, and

meansfor applying apotential between said further conductive means and said conductive means on the side of said insulating means adjacent said drop charging position to establish an electric field therebetween to enable ions passing through said apertures to bombard a drop. 

1. In an ink drop printing system of the type wherein drops of ink are formed in a serial stream, and are emitted along a path toward a recording medium, said drops have charges applied to them in accordance with signals from a video source at a charging position along said path, said drops thereafter passing between two deflection electrodes which deflect the drops a distance determined by the amplitude of the charges thereon, and said drops finally coming to rest upon said recording medium, the improvement in charging said drops comprising: a source of ions, means for establishing a field for bombarding each drop with ions as it passes through said charging position, and means for applying signals from said video source to said means for establishing a field for controlling said field for determining the amount of charge on each drop.
 2. In an ink drop printing system as recited in claim 1 wherein there is included: means responsive to the presence of ink drops at a location prior to said charging position for generating timing signals responsive thereto, and means for timing the application of signals for controlling said field responsive to said timing signals.
 3. In an ink drop printing system as recited in claim 1 wherein said means for establishing a field comprises: blocking means interposed between said source of ions and the path of said drops at said charging position to block the access of ions from said source from said path of said drops, said blocking means having an aperture therethrough sized to afford ions access to a drop at a time, and a first conductive means surrounding said aperture on the side of said blocking means adjacent said source of ions, said means for applying signals from said video source to said means for establishing a field includes: means for applying said signals between said source of ions and said first conductive means surrounding said aperture.
 4. In an ink drop system as recited in claim 3 wherein said means for establishing a field for bombarding each drop with ions further includes: a second conductive means surrounding said aperture on the side of said blocking means, adjacent the path of said drops, a third conductive means positioned opposite said second conductive means and spaced therefrom to permit said stream of drops to pass therebetween, and means for biasing said second and third conductive means relative to said first conductive means to establish fields which direct ions entering said aperture at the path of said drops.
 5. In an ink drop system as recited in claim 1 wherein said means for bombarding each drop with ions as it passes through said charging position includes: a blocking means interposed between said source of ions and the path of said drops at said charging position to block the access from said source from said path of said drops, saiD blocking means having a plurality of apertures therethrough and spaced along the path of said drops and sized to afford ions access successively to a drop as it moves along said path through said charging position, and a separate first conductive means surrounding each of said plurality of apertures on the side of said blocking means adjacent said source of ions, said means for applying said signals from said video source to said means for establishing a field includes, analog-to-digital means for converting each of said signals from said video source into a binary code having as many bit signals as there are apertures in said blocking means, and means for applying the bit signals representative of a video signal between said source of ions and each of said separate first conductive means successively to charge a drop passing through said charging position.
 6. In an ink drop system as recited in claim 5 wherein said means for applying the bit signal representative of a video signal between said source of ions and each of said separate first conductive means successively includes: a shift register for each of said plurality of apertures, means for applying the output of each shift register to a separate one of said first conductive means, means for applying each bit signal to the input of a different one of said shift registers, means for detecting the presence of a drop prior to its entrance into said charging position, and producing a timing signal representative thereof, and means for applying said timing signal to each of said shift registers to cause them to advance responsive thereto.
 7. In an ink drop printing system of the type wherein drops of ink are formed in a serial stream, and are emitted along a path toward a recording medium, said drops have charges applied to them in accordance with signals from a video source at a charging position along said path, said drops thereafter passing between two deflection electrodes which deflect the drops a distance determined by the amplitude of the charges thereon, and said drops finally coming to rest upon said recording medium, the improvement in charging said drops comprising: a source of ions, conductive grid means interposed between the source of ions and said charging position, and means for applying signals from said video source to said conductive grid means for controlling responsive thereto the amount of ions which can pass through said conductive grid means to charge a drop passing through said charging position.
 8. In an ink drop system as recited in claim 7 wherein said conductive grid means comprises: an insulating blocking means having an aperture therethrough, and conductive means surrounding said aperture on each surface of said insulating blocking means.
 9. In an ink drop system as recited in claim 7 wherein said conductive grid means comprises: an insulating blocking means having an aperture therethrough, a separate conductive means surrounding each aperture on the surface of said insulating blocking means adjacent said ion source, and a conductieve means surrounding each aperture on the other side.
 10. In an ink drop system as recited in claim 9 wherein said means for applying signals from said video source to said conductive grid means comprises: means for converting each of said signals from said video source into a binary code having as many bit signals as there are apertures in said insulating blocking means, means for applying the bit signals representative of a video signal between said source of ions and each of said separate conductive means successively to charge a drop passing through said charging position.
 11. In an ink drop system as recited in claim 10 wherein said means for applying the bit signals representative of a video signal between said source of ions and each of said separate conductive means successively includes: means responsive to the presence of drops priOr to entering said charging position for generating timing signals, a separate delay means for each aperture, each delay means having its input connected to receive one of the bit signals in a binary code representative of a video signal and its output connected to apply a bit signal to a separate one of said separate conductive means, and means for applying said timing signals to each of said separate delay means to enable said separate delay means to successively apply a bit signal to a conductive means as a drop passes the aperture surrounded by said conductive means.
 12. In an ink drop system as recited in claim 8 wherein there is included a further conductive means positioned opposite said insulating blocking means at said charging position to permit drops to pass therebetween, and means for applying a potential between said further conductive means and said conductive means surrounding the apertures of said insulating means to establish an electric field therebetween for enabling ions passing through said aperture to bombard a drop opposite said aperture.
 13. In an ink drop system as recited in claim 9 wherein there is included a further conductive means positioned opposite said insulating blocking means at said charging position to permit drops to pass therebetween, and means for applying a potential between said further conductive means and said conductive means on the side of said insulating means adjacent said drop charging position to establish an electric field therebetween to enable ions passing through said apertures to bombard a drop. 